2 gang switch -> 2 gang dimmer

31 Oct 2005
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United Kingdom
Need some help please with matching the wires from the current 2 gang wall switch to a new dimmer.

Current wall switch has:
[code:1] ______________
| |
| L1 L3 L2 |
| |
| L3 L2 L1 |

Cable 1: black to top L1, red to top L3
Cable 2: black to top L2, red to bottom L1
Cable 3: black to bottom L2, red to bottom L1

The new 2 gang, 2 way dimmer is to be wired 1 way, since there is only one switch for each of the lights it will control. The dimmer has 2 sets of (~ L1 L2). How should the wires go on the dimmer?

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This is how the old to new labelling is most likely to be:
L1 ~
L2 L1
L3 L2
Top L1, bottom L2 & L3 will most likely form one of the old switches,
Bottom L1, top L2 & L3 will form the other.

Your existing setup appears to have 2x 2way circuits, is this correct?
Those conversions do seem to make sense when I draw them in a diagram.

As for whether it's a 2-way circuit I'm not sure. Each switch controls one light, and each of those lights has only the one switch. How else do I tell, and what are the implications?
It is the amount of wires and how they are connected which behind the existing switch which is making me think there is more than one switch controlling each light.
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Switch one (top L1, bottom L2, L3) controls an outside light and the other switch controls a interior ceiling light.

On closer examination it seems that Cable 3 in my original post goes from the switch straight through the brick wall directly to the outside light.

So does that mean:
Cable 1 is incoming power
Cable 2 is the switch cable for the ceiling light
Cable 3 is outgoing power to the outside light
The inside light appears to me to have been connected for 2 way operation, hence the 3 terminals used. If you notice the diagonal line down the centre of the switch, this separates out the two switches. I can't see the wire going directly to the outside light as it doesn't appear to have a neutral - unless your outside light only works when the inside one is turned off (which would mean the wiring at the switch is wrong and I'll take it back about the 2 way operation too!!).

from the look of that picture, the outside light only works when the inside light is switched off.... ???????

switch 2 is switching neutrals???

if you have a multimeter, please check the voltage between earth and the 2 black wires on switch 2..

there should be no voltage ( or maybe a small voltage, but not 240.. )
Also slapped wrists for not using green/yellow sheath for the earth!! ;)
I'm afraid I don't have a multimeter handy at the moment. Even if I did I'm not sure how to use one :(

I checked the operation of both switches and found that both lights will switch indpendently on and off, regardless of the state of the other.

Is it possible to work out from this how to wire each light for one way operation to the dimmer?
how far from me is berkshire?

I can't work out what the hell is going on from your description and the photo...
I must admit I am also struggling to figure out what is going on there, possibly that when the switch has been disconnected in the past it has had the permanent lives muddled up?? Still, if it was designed for single way switching there would only normally be 2 cables present in this configuration. Can you trace where the wires go and what they connect to?
To connect the dimmer switch the same as the existing circuit is wired means transposing the wires L1 to ~ , L2 to L1 , L3 to L2. Do you really want a dimmer on your outside light?
Ok, I must apologise, I have just found another switch. Lived here for nearly 2 yrs and never noticed it! :oops:

There is another switch in the room that seems to override the other two. If this switch is off, then neither of the other two work. If it's on, then the other two work normally.

Does that make any more sense now?

As far as using a dimmer for the outside light goes, my brief look in B&Q found no 2 gang switches with only 1 dimmer. We don't use that outside light anyway so I'm not bothered.
Hi, not sure whether I'm out of favour or my last post just got missed. I found the 3rd switch that was related to the cabling picture I posted so I'm hoping that makes the picture clearer.

I'm looking for confirmation that Spark123's last post of [code:1]L1 to ~ , L2 to L1 , L3 to L2[/code:1] is still valid.


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